Aluminum fan blade construction with welded cover

ABSTRACT

An airfoil includes, among other possible things, a main body extending between a leading edge and a trailing edge. Channels are formed into the main body, with a plurality of ribs extending intermediate the channels. A cover skin is attached to the main body. The cover skin is welded to the main body with a weld at outer edges. An adhesive is placed between inner surfaces of the cover skin and the main body. The adhesive is deposited inwardly of the outer edges of the cover skin. A method of constructing an airfoil is also disclosed as is a gas turbine engine.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/343,025, filed Jan. 4, 2012.

BACKGROUND

This application relates to a hollow fan blade construction and methodof construction wherein a cover is welded to a main blade body, andwherein the cover is also attached to internal components by anadhesive.

Gas turbine engines are known, and typically include a fan deliveringair into a compressor section. The air is compressed in the compressorsection, delivered into a combustion section, mixed with fuel andburned. Products of this combustion pass downstream over turbine rotors,driving the turbine rotors to rotate.

The turbine rotors in turn drive the compressor rotors and the fan. Onerecent development in gas turbine engines is a so-called “geared” fan. Agear reduction is provided between a turbine spool driving a lowpressure compressor and the fan. In this manner, the speed of the fancan be varied relative to the speed of the low pressure compressor. Withsuch an arrangement, larger fan blades can be utilized.

To reduce the weight associated with the larger fan blades, hollowaluminum fan blades arrangements have been proposed. These hollow bladestypically have a number of hollow channels which may or may not includea light weight filler. A cover skin is typically adhesively bonded tothe main body to enclose the hollow fan blade.

SUMMARY

In a featured embodiment, an airfoil has a main body extending between aleading edge and a trailing edge, and channels formed into the mainbody, with a plurality of ribs extending intermediate the channels. Acover skin is attached to the main body, the cover skin being welded tothe main body with a weld at outer edges of the cover skin, and anadhesive between inner surfaces of the cover skin and the main body,with the adhesive being deposited inwardly of the outer edges of thecover skin.

In another embodiment according to the previous embodiment, the mainbody defines a ledge having outer edges formed into the main body at atleast one face. The cover skin sits on the ledge, with the adhesivebeing deposited inwardly of the ledge such that the adhesive is notadjacent to the weld.

In another embodiment according to any of the previous embodiments, theadhesive extends outwardly to inner extents of the ledge.

In another embodiment according to any of the previous embodiments, theadhesive is deposited inwardly of inner extents of the ledge.

In another embodiment according to any of the previous embodiments, amaterial is positioned in at least one of the channels, and the adhesiveis formed over at least portions of the material and portions of theribs.

In another embodiment according to any of the previous embodiments, thecover skin has thicker edges, such that when welded to the main body,the thicker edges provide strengthened regions.

In another embodiment according to any of the previous embodiments, theweld joint is provided by stir welding.

In another embodiment according to any of the previous embodiments, thechannels extend into the main body to a closed end from an open end,such that there is a single cover skin closing off the channels.

In another embodiment according to any of the previous embodiments, theairfoil is part of a fan blade for a gas turbine engine.

In another embodiment according to any of the previous embodiments, theairfoil extends radially outwardly from a dovetail.

In another featured embodiment, a method of constructing an airfoilincludes providing adhesive on a main body extending between a leadingedge and a trailing edge, and having channels formed into the main body,with a plurality of ribs extending intermediate the channels. A coverskin is placed over the channels, and welds the cover skin to the mainbody. The adhesive is provided such that it will be spaced inwardly ofthe location of a weld joint.

In another embodiment according to the previous embodiment, the mainbody defines a ledge having outer edges formed into the main body at atleast one face. The cover skin sits on the ledge, with the adhesivedeposited inwardly of the ledge such that the adhesive is not adjacentto the weld joint.

In another embodiment according to any of the previous embodiments, theadhesive extends outwardly to inner extents of the ledge.

In another embodiment according to any of the previous embodiments, theadhesive is deposited inwardly of inner extents of the ledge.

In another embodiment according to any of the previous embodiments, thecover skin has thicker edges, such that when welded to the main body,the thicker edges provide strengthened regions.

In another featured embodiment, a gas turbine engine comprises a fansection delivering air into a compressor section. Air compressed by thecompressor section is delivered into a combustor where it is mixed withfuel and combusted. Products of the combustion pass downstream over aturbine section. The fan section includes a plurality of fan blades,with the fan blades comprising a main body extending between a leadingedge and a trailing edge, and channels formed into the main body. Thefan blade has a dovetail and an airfoil extending radially outwardlyfrom the dovetail. A cover skin is attached to the main body, and closesoff the channels. The cover skin is welded to the main body with a weldat outer edges of the cover skin. An adhesive is between inner surfacesof the cover skin and the main body, and is deposited inwardly of theedges of the cover skin.

In another embodiment according to the previous embodiment, the mainbody defines a ledge having outer edges formed into the main body at atleast one face. The cover skin sits on the ledge, with the adhesivedeposited inwardly of the ledge such that the adhesive is not adjacentto the weld.

In another embodiment according to any of the previous embodiments, theadhesive extends outwardly to inner extents of the ledge.

In another embodiment according to any of the previous embodiments, theadhesive is deposited inwardly of inner extents of the ledge.

In another embodiment according to any of the previous embodiments, afoam material is positioned in at least one of the channels, and theadhesive being formed over at least portions of the foam and portions ofthe ribs.

In another embodiment according to any of the previous embodiments, thecover skin has thicker edges, such that when welded to the main body,the thicker edges provide strengthened regions.

These and other features of the invention would be better understoodfrom the following specifications and drawings, the following of whichis a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a typical gas turbine engine.

FIG. 1B shows a fan blade according to this invention.

FIG. 1C is a view of a fan blade mounted in a fan rotor.

FIG. 2 is a cross-sectional view along line 2-2 of FIG. 1B.

FIG. 3 shows the internal detail of the fan blade.

FIG. 4 shows an assembled fan blade, with a cover attached.

FIG. 5 shows an alternative to the FIG. 4 adhesive arrangement.

FIG. 6A shows a first step in assembling the cover to the blade.

FIG. 6B shows a subsequent step.

FIG. 6C shows the final arrangement.

DETAILED DESCRIPTION

A gas turbine engine 210 is shown in FIG. 1A. As shown, the engine 210includes a fan 250 (which includes a plurality of fan blades 20), acompressor section 254 (which includes both a low pressure compressor256 and a high pressure compressor 258), a combustor 260, and a turbinesection 262 (which includes both a high pressure turbine 264 and a lowpressure turbine 266). The fan 250 delivers air into compressor section254. Air compressed by the compressor section is delivered intocombustor 260. Products of the combustion in the combustor passdownstream over turbine section 262. The high pressure compressor 258 isdriven, via a first spool 268, by the high pressure turbine 264. The lowpressure compressor 256 is driven, via a second spool 270, by the lowpressure turbine 266. Also driven by the low pressure turbine 266 arethe fan blades 20 of the fan 250, which fan is coupled to the secondspool 270 via a gear 272. While an engine with two spools is shown, theapplication extends to three spool engines, and engines havingalternative constructions.

A fan blade 20 is illustrated in FIG. 1B having an airfoil 18 extendingradially outwardly from a dovetail 24. A leading edge 21 and a trailingedge 22 define the forward and rear limits of the airfoil 18.

As shown in FIG. 1C, a fan rotor 16 receives the dovetail 24 to mountthe fan blade with the airfoil 18 extending radially outwardly. As therotor is driven to rotate, it carries the fan blade with it. There arehigher stresses in fan blade 20 adjacent to the rotor 16 then occurradially outwardly.

FIG. 2 shows a cross-section of the fan blade 20, at the airfoil 18. Asshown, the leading edge 21 carries a sheath 37 secured to a main body28. A cover skin 32 closes off cavities or channels 30 in the main body28. The main body 28 and the skin 32 may all be formed of aluminum orvarious aluminum alloys. Other materials, such as titanium, titaniumalloys or appropriate metals may alternatively be utilized. The sheath37 is typically formed of a titanium alloy.

In addition, while the fan blade is shown having one cover, and thechannels 30 having a closed inner end 34, it is also possible that themain body would provide a channel extending across its entire thickness,with covers at each side.

As shown, a plurality of ribs 26 separate channels 30 in thecross-section illustrated in FIG. 2. As shown, filler material 100 maybe deposited within the channels 30. The filler material 100 wouldtypically be of a lighter weight than the main body 28. As one example,an aluminum foam may be used as material 100. Other light weightfilters, such as honeycomb material, or other materials, may be used.

FIG. 3 shows the main body 28. There are a plurality of channels 30spaced from the front or leading edge 21 to the back or trailing edge22. As shown, some of the channels 30 extend generally radiallyupwardly. Other channels, such as channel 40, bend toward the leadingedge 21. Channel 41 simply extends generally from the middle of the mainbody 28 toward the leading edge 21. Channel 300 receives no material.Any or all of the channels may be left empty.

As shown in FIG. 3, the main body 28 includes a ledge 400 defined byledge edge 310, 312, 316 and 318. Edges 310 and 312 are also shown inFIG. 2 at the forward and rearward ends. As is clear, from FIG. 2 thecover 32 sits on ledge 400 when assembled. As shown in FIG. 3, anoutline 314 of adhesive is positioned laterally inwardly from the edges310, 312, 316 and 318.

As shown in FIG. 4, when the cover skin 32 is assembled on the main body28, it sits adjacent ends of ledge 400. Then, friction stir welding asshown at 320 is provided along the entire periphery of the cover 32 tosecure the cover to the main body.

Since the adhesive is positioned inwardly from edges 310, 312, 316 and318, the adhesive will not move into the area adjacent to the frictionstir weld 320, where it might reduce the weld quality.

FIG. 5 shows an alternative wherein there is a greater area of adhesive321, with the adhesive moving generally outwardly to an outline 323 thatfills all of the area inwardly of ledge 400. If the adhesive has beenpositioned such that it extends on to the ledge 400, it can be removedprior to welding of the cover. In addition, a worker in this art shouldrecognize that when placing cover 32 onto the main body 18, it ispossible that adhesive will be squeezed outwardly, and this should betaken into account when designing the coverage area of the adhesive.

As a further alternative, a braze material could be deposited along theinner edges of the ledge to block adhesive. In addition, the brazematerial can be selected such that it will melt at temperatures belowthat of the welding such that the braze material will assist in forminga stronger bond between the cover and the main body.

While an embodiment is shown having a single cover, and with thechannels 30 having closed back ends 34, this application would alsoextend to a main body having covers at each of the two sides, with thechannels extending through the entire width of the blade.

FIG. 6A shows an alternative embodiment the cover skin 432 as initiallyplaced on the main body 28. As shown at the edge 312, there is anenlarged portion 322, which is thicker than the nominal portions of thecover skin 432.

FIG. 6B shows the application of the friction stir weld through a tool360. As shown in FIG. 6C, after this operation, the material from themain body 28 and the enlarged portion 322 have generally intermixed.That is, the thicker area provides a stronger cross-section, orstrengthened regions, and will result in less stress at this combinedarea 350.

While a fan blade is specifically disclosed, it should be understoodthat aspects of this disclosure would extend to any number of other typeof airfoils.

Although embodiments of this invention have been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

The invention claimed is:
 1. An airfoil comprising: a main bodyextending between a leading edge and a trailing edge, and channelsformed into said main body, with a plurality of ribs extendingintermediate the channels; and a cover skin attached to said main body,said cover skin being welded to said main body with a weld at outeredges of said cover skin, and an adhesive between inner surfaces of saidcover skin and said main body, with said adhesive being depositedinwardly of said outer edges of said cover skin, said main body and saidcover skin being formed of one of aluminum, aluminum alloys, titanium,or titanium alloys.
 2. The airfoil as set forth in claim 1, wherein saidmain body defines a ledge having outer edges formed into said main bodyat at least one face, and said cover skin sitting on said ledge, withsaid adhesive being deposited inwardly of said ledge such that saidadhesive is not adjacent to said weld.
 3. The airfoil as set forth inclaim 2, wherein said adhesive extends outwardly to inner extents ofsaid ledge.
 4. The airfoil as set forth in claim 2 wherein said adhesiveis deposited inwardly of inner extents of said ledge.
 5. The airfoil asset forth in claim 1, wherein a foam material is positioned in at leastone of said channels, and said adhesive being formed over at leastportions of said foam material and portions of said ribs.
 6. The airfoilas set forth in claim 1, wherein said weld joint is provided by stirwelding.
 7. The airfoil as set forth in claim 1, wherein said channelsextend into the main body to a closed end from an open end, such thatthere is a single cover skin closing off said channels.
 8. The airfoilas set forth in claim 1, wherein said airfoil is part of a fan blade fora gas turbine engine.
 9. The airfoil as set forth in claim 1, whereinsaid airfoil extends radially outwardly from a dovetail.
 10. A gasturbine engine comprising: a fan section delivering air into acompressor section, air compressed by the compressor section deliveredinto a combustor where it is mixed with fuel and combusted, products ofthe combustion pass downstream over a turbine section; said fan sectionincluding a plurality of fan blades, with said fan blades comprising amain body extending between a leading edge and a trailing edge, andchannels formed into said main body, the fan blade having a dovetail,and an airfoil extending radially outwardly from said dovetail; and acover skin attached to said main body, and closing off said channels,said cover skin being welded to said main body with a weld at outeredges of said cover skin, and an adhesive between inner surfaces of saidcover skin and said main body, with said adhesive being depositedinwardly of said edges of said cover skin, said main body and said coverskin being formed of one of aluminum, aluminum alloys, titanium, ortitanium alloys.
 11. The engine as set forth in claim 10, wherein saidmain body defines a ledge having outer edges formed into said main bodyat at least one face, and said cover skin sitting on said ledge, withsaid adhesive being deposited inwardly of said ledge such that saidadhesive is not adjacent to said weld.
 12. The engine as set forth inclaim 11, wherein said adhesive extends outwardly to inner extents ofsaid ledge.
 13. The engine as set forth in claim 11 wherein saidadhesive is deposited inwardly of inner extents of said ledge.
 14. Theengine as set forth in claim 10, wherein a foam material is positionedin at least one of said channels, and said adhesive being formed over atleast portions of said foam and portions of said ribs.